Roof bolt system

Abstract

A mechanical anchor including an expansion shell and an expansion plug positioned in the shell is engaged with the end of a bar having helically extending rib segments formed on the outer surface of the bar. The expansion plug has an internal bore defining a wall having a configuration to receive and mate with the helically extending rib segments formed on the outer surface of the bar. The mechanical anchor and a portion of the bar are inserted in a bore hole drilled in a rock formation and, upon rotation of the bar in a preselected direction, the expansion plug nonrotatably moves down the bar to expand the shell into engagement with the bore hole wall. As the shell engages the bore hole wall, the bar is mechanically anchored within the bore hole by the mechanical anchor. If it is desired to combine mechanical and chemical anchoring of the bar within the bore hole, the expansion plug is provided with a displaceable stop means positioned in the expansion plug bore, and a curable, two component bonding material is positioned in the bore hole ahead of the mechanical anchor. The stop means permits initial rotation of the mechanical anchor and ribbed bar within the bore hole to mix the bonding material components before the expansion shell is expanded. In addition, various other embodiments of a bar having helically extending rib segments formed on the outer surface of the bar and anchored in a bore hole are disclosed herein.

I claim: 
     
       1. An apparatus for anchoring a ribbed bar in a bore hole comprising, an elongated bar adapted for use in a bore hole, said bar having a plurality of helically extending discontinuous rib segments formed on the outer surface of said bar, said discontinuous rib segments forming a thread on said bar,   an expansion plug having first and second end portions and an outer wall surface, said expansion plug having a bore therethrough defining an inner wall extending from said first end portion to said second end portion,   said expansion plug inner wall having a continuous helical thread portion to receive and mate with certain of said helically extending discontinuous rib segments formed on said outer surface of said bar,   an expansion shell having a base portion and a plurality of longitudinal fingers extending from said base portion, said base portion having an opening therethrough for receiving a portion of said bar,   said plurality of fingers each having an outer surface for engaging the wall of said bore hole and an inner surface, a portion of said expansion plug outer wall surface abutting said plurality of fingers inner surfaces,   a portion of said bar extending through said opening in said expansion shell base portion and surrounded by said longitudinal fingers, portions of said bar discontinuous rib segments engaging said continuous helical thread portion of said expansion plug, and   means for rotating said elongated bar relative to said expansion plug to threadably move said bar discontinuous rib segments in said expansion plug continuous helical thread portion and move said expansion plug on said elongated bar to more rapidly and with fewer revolutions expand said expansion shell fingers and anchor said expansion shell and said bar in said bore hole and apply a tension to said ribbed bar.   
     
     
       2. An apparatus for anchoring a ribbed bar in a bore hole as set forth in claim 1 which includes, a stop means positioned in said expansion plug bore,   a portion of said bar extending through said opening in said expansion shell base portion and engaging said expansion plug continuous helical thread portion and abutting said stop means, said stop means preventing longitudinal relative movement between said bar and said expansion plug to permit said bar, said expansion shell and said expansion plug to rotate together within said bore hole upon application of a preselected torque to said bar, and   said bar arranged to displace said stop means from said expansion plug bore upon applying to said bar a torque in excess of a preselected torque so that additional discontinuous ribbed segments on said bar further engage said expansion plug and said expansion plug nonrotatably moves on said bar to expand said expansion shell fingers and anchor said expansion shell and said bar in said bore hole and apply a tension to said bar.   
     
     
       3. An apparatus for anchoring a ribbed bar in a bore hole as set forth in claim 1 which includes, bonding material positioned in an unmixed condition in said bore hole ahead of said expansion shell and said expansion plug,   said stop means positioned in said expansion plug bore operable to prevent further engagement between said bar and said expansion plug to cause said bar, said expansion shell and said expansion plug to rotate together within said bore hole to mix said bonding material in said bore hole,   said stop means arranged to be displaced from said expansion plug bore when said mixed bonding material exerts a force resisting rotation on said expansion shell and said expansion plug, thereby permitting rotation of said bar relative to said expansion plug and said expansion shell, and   said expansion plug being nonrotatably movable on said bar after said stop means is displaced from said expansion plug bore to expand said fingers into engagement with the wall of said bore hole.   
     
     
       4. An apparatus for anchoring a ribbed bar in a bore hole as set forth in claim 1 in which, said continuous helical thread portion in said expansion plug inner wall extends completely through said expansion plug bore from said first end portion to said second end portion.   
     
     
       5. An apparatus for anchoring a ribbed bar in a bore hole as set forth in claim 1 in which, the depth of the recessed portions between said helical threads in said expansion plug inner wall is greater than the height of each discontinuous rib segment extending from said bar outer surface.   
     
     
       6. An apparatus for anchoring a ribbed bar in a bore hole as set forth in claim 1 in which, each of said discontinuous rib segments includes a pair of flanks each extending from said bar outer surface at substantially the same included angle.   
     
     
       7. A method for anchoring a ribbed bar in a bore hole comprising the steps of, providing an elongated bar having a plurality of helically extending discontinuous rib segments formed on the outer surface of said bar,   positioning an expansion shell having a base portion with an opening therethrough and a plurality of longitudinal fingers extending from said base portion in abutting relation with an outer wall of said expansion plug so that a portion of each said finger contacts said expansion plug outer wall,   providing said expansion plug with a bore therethrough, said bore defining an inner wall having a continuous helical internal thread to receive and mate with a portion of said helically extending discontinuous rib segments on said bar outer surface,   passing a portion of said bar through said opening in said expanion shell base portion, said portion of said bar surrounded by said plurality of longitudinal fingers,   engaging a portion of said helically extending rib segments on said bar with said internal threaded portion of said expansion plug,   positioning said expansion shell and said expansion plug in a bore hole,   rotating said expansion plug and said expansion shell in a predetermined direction in said bore hole upon rotation of said bar, and   engaging additional discontinuous segments on said bar to said internal thread of said expansion plug, said expansion plug nonrotatably moving longitudinally on said bar to more rapidly and with fewer revolutions expand said expansion shell fingers and anchor said expansion shell and said bar in said bore hole and apply a tension to said bar.   
     
     
       8. A method for anchoring a ribbed bar in a bore hole as set forth in claim 7 including the further steps of, positioning a stop means in said expansion plug bore,   passing a portion of said bar through said expansion shell base portion opening and engaging said expansion plug with said bar until said bar abuts said stop means, said stop means preventing further engagement between said bar and said expansion plug to permit said bar, said expansion shell and said expansion plug to rotate together within said bore hole upon application of a preselected torque to said bar, and   displacing said stop means from said expansion plug bore upon applying to said bar a torque in excess of said preselected torque so that said bar further engages said expansion plug and said expansion plug nonrotatably moves on said bar to expand said expansion shell fingers into engagement with a bore hole wall.   
     
     
       9. A method for anchoring a ribbed bar in a bore hole as set forth in claim 7 including the further steps of, positioning a bonding material in an unmixed condition in said bore hole ahead of said expansion shell and said expansion plug,   preventing further engagement between said bar and said expansion plug with said stop means,   rotating said bar, said expansion shell and said expansion plug as a unit within said bore hole to mix said bonding material,   displacing said stop means from said expansion plug bore when said mixed bonding material exerts a force resisting rotation on said expansion shell and said expansion plug, thereby permitting rotation of said bar relative to said expansion plug and said expansion shell, and   nonrotatably moving said expansion plug on said bar after said stop means is displaced from said expansion plug bore to expand said fingers into engagement with a bore hole wall.   
     
     
       10. An apparatus for anchoring a ribbed bar in a bore hole comprising, an elongated bar adapted for use in a bore hole, said bar having helically extending discontinuous rib segments formed on the outer surface of said bar, said bar having a first end portion adapted to be positioned in a bore hole and a second end portion, and   engaging means having a continuous internal thread, said engaging means threadedly secured to said discontinuous rib segments of said bar at said second end portion operable to engage a rotating means to permit rotation of said bar within said bore hole by said rotating means.   
     
     
       11. An apparatus for anchoring a ribbed bar in a bore hole as set forth in claim 10 which includes, an expansion shell and expansion plug assembly engaged with said elongated bar at said first end portion, said expansion plug having an internal bore defining a wall having a continuous internal thread to receive and mate with a portion of said helically extending discontinuous rib segments formed on said outer surface of said bar.   
     
     
       12. An apparatus for anchoring a ribbed bar in a bore hole as set forth in claim 10 in which said engaging means includes, a tensioning nut engaged with said bar at said second end portion, said tensioning nut having an internal bore defining a wall having a configuration to receive and mate with said helically extending rib segments formed on said outer surface of said bar, and   a stop means positioned in said tensioning nut bore to permit rotation of said bar in said bore hole by said rotating means.   
     
     
       13. An apparatus for anchoring a ribbed bar in a bore hole as set forth in claim 10 in which said engaging means includes, a cap nut engaging with said bar at said second end portion, said cap nut having an internal bore extending a preselected distance into said cap nut, said bore defining a wall having a configuration to receive and mate with said helically extending rib segments formed on said outer surface of said bar,   said cap nut having outer wall surface adjacent said internal bore to close said bore and thereby limit the amount of engagement of said cap nut on said ribbed bar second end portion.